Pnuematic-to-hydraulic brake systems have come into extensive use in railcar and other types of braking systems in recent years. In many instances, it has been found desirable to provide an independent means for applying and locking the brakes when the car is not connected to a source of pressurized air such as would conventionally be used to actuate the brakes. Such independent parking brake means permit each car to be slowed, stopped and restrained in a chosen location by a single crewman. Copending application Ser. No. 484,197 is an example of a recently developed system for articulated railcars incorporating a new type of parking brake actuator. As discussed in Ser. No. 484,197, parking brake systems may include means for applying, locking and unlocking the parking brakes which are actuated by a handwheel or similar device located conveniently on the car. U.S. Pat. No. 3,586,138 discloses a hydraulically operated brake locking mechanism suitable for use in these applications.
The prior art systems such as that of U.S. Pat. No. 3,586,138 for actuating and locking railcar parking brakes may create problems in use since it is frequently the case that the parking brake has not been fully unlocked and released by a crewman before an attempt is made to move the car. Obviously, this can cause numerous delays to locate the stuck brakes, undue brake wear if some movement does occur and similar deleterious effects.
An object of the invention is to provide a system for ensuring parking brake release which will positively unlock the parking brake locking mechanism to permit car movement yet will not interfere with subsequent operations of the parking brake system.
Another object of the invention is to provide a system for ensuring parking brake release which will permit parking brake application even when the release ensuring system is actuated.
Another object of the invention is to provide a brake release ensuring system which is automatic and operates from available sources of pressurized fluid such as the conventional brake pipe pressure system of prior art railcars.
One skilled in the art will realize that some or all of the above objects are realized by the invention disclosed herein and may recognize other objects of the invention not specifically set forth; however, the scope of the invention is to be limited only by the claims presented hereafter.